Fix task timing race in setnsec3param()
When setnsec3param() is schedule from zone_postload() there's no
guarantee that zone->db
is not NULL
yet. Thus when the
setnsec3param() is called, we need to check for zone->db
existence and
reschedule the task, because calling rss_post()
on a zone with empty
.db
ends up with no-op (the function just returns).
Closes #2636 (closed)
Edited by Ondřej Surý